Petrology of Mafic and Intermediate-Composition Magmas Associated with Rhyolite Ash-flow Volcanism, Sierra Madre Occidental

本研究探讨了镁铁质和中间- 托莫奇克流纹岩成因中的混合岩浆 火山中心（TVC），地层剖面是 火山活动历史最完整的地方 在马德雷山脉已知的火山爆发中心 西方。 TVC最近的实地和年表工作 表明两种不同的岩性，斑状二辉石 安山岩和贫结晶玄武安山岩 供给大量流纹岩的岩浆系统的成分 火山灰流喷发 它们之间的遗传关系 岩性和韵律是允许的，但很差 受现有数据的限制。 本研究的主要目的是 将通过以下方式进一步评估这种关系： （a）矿物学、同位素（Sr、Nd）的比较和建模， 所有岩石类型之间的地球化学变化，以及 (b)混合后塌陷熔岩的岩石学研究， 描述了地下储层的深基性部分， 拉斯瓦拉斯破火山口，与挤压玄武岩比较 安山岩 结果将限制有关的起源模型 流纹岩和相关的镁铁质岩浆， 被认为是世界上最大的“流纹岩为主“的火山 领域 结果也将是重要的模型连接风格的 火山活动与构造体制，以及我们对 与大体积的演化相关的过程 火山口下的水库

This study addresses the role of mafic and intermediate- composition magmas in the genesis of rhyolites at the Tomochic volcanic center (TVC), where the stratigraphic section is the most complete and where the history of volcanism is best documented among known eruptive centers in the Sierra Madre Occidental. Recent field and chronologic work at the TVC has indicated that two distinct lithologies, porphyritic two-pyroxene andesite and crystal-poor basaltic andesite, were important components of the magma systems that fed large-volume rhyolite ash-flow eruptions. A genetic relationship between these lithologies and the rhyolites is allowed, but is poorly constrained, by available data. The principal goal of this study will be to evaluate that relationship further, via: (a)comparison and modeling of mineralogic, isotopic (Sr, Nd), and geochemical variations among all rock types, and (b) petrologic study of hybrid post-collapse lavas, to characterize the deep, mafic parts of the reservoir beneath the Las Varas caldera, for comparison with extruded basaltic andesite. Results will constrain model pertaining to the genesis of rhyolites, and of associated, more mafic magmas, in what is considered the world's largest "rhyolite-dominated"volcanic field. Results will also be important to models linking style of volcanism with tectonic regime, and to our understanding of processes associated with the evolution of large-volume subcaldera reservoirs.